The spring brake actuators used nowadays are generally separated into two groups. These are the diaphragm-diaphragm spring brake actuators and diaphragm-piston spring brake actuators. The spring brake actuators are used in heavy commercial vehicles (such as trucks, trailers, lorries, busses etc.)
The diaphragm-diaphragm brake chambers, comprise a service brake chamber which is engaged in normal driving conditions and a parking chamber that is engaged when there is air leakage or when the air is released on purpose (pulling the handbrake). The service chamber carries out the braking process when the vehicle is being slowed down or stopped, and the parking chamber is used when the vehicle is fixed. In other words when the service chamber functions when the foot brake is actuated and the parking chamber functions when the hand brake of the vehicle is actuated.
The parking chamber is the section between the emergency diaphragm and the adapter plate formed by the connection of the adapter plate and the spring housing in any kind or shaped connection. The parking chamber section of the brake actuator generally comprises a strong spring, an emergency diaphragm, an intermediate shaft flange and a return spring. When the vehicle is moving, pressurized air which is provided continuously by the compressor, is present inside the parking chamber. The pressurized air, ensures that the emergency spring is compressed as in the brake off position.
When there is a pressure decrease in the vehicle air system due to any kind of reason or when the vehicle is being parked (the handbrake is “on” position), the air pressure in the parking chamber decreases or is completely released. In such a case the flange can no longer compress the spring and the spring is released. Once the spring is released, the force of the spring is transmitted to the service chamber by means of the intermediate shaft located at the center of the adapter plate and from here to the wheels of the vehicle.
Several designs have been created in order to solve the abrasion problem of the center bearing of adapter plate. However the designs that have been created, are not directed to eliminate the reason that causes the abrasion but are aimed to decrease said abrasion. In some of these designs plastic bearing materials and in others metallic bearing materials are used.
In the application numbered TR 2008 07310 Y of the prior art, it has been aimed to decrease the abrasion of the intermediate shaft by friction between adapter plate and intermediate shaft, when it is in motion, by using a plastic bearing sealing member (14), plastic bearing (13), o-ring, o-ring channels, piston rings, ring channels and connector shells. The task of each of the sealing members mentioned above is bearing the intermediate shaft and to prevent the unwanted decrease of air pressure inside the parking chamber by preventing air flow to service chamber from parking chamber by means of the o-ring used on circumference. However this design is quite complex and the number and variety of the connection means used are high, thus leading to high installation and production costs.
In the TR2002 00762 Y application the adapter plate itself has been used instead of using a separate bearing means. The sealing means mounted to the channels that open up to the center of adapter plate provide impermeability.
In the known state of the art, v-shaped sealing means mounted into the shells on the adapter plate as mentioned in the patent application file numbered CA2550930A1 have been used in order to provide said bearing and sealing.
In the invention subject to the application number TR 2010/07609 in the known state of the art, it has been aimed to decrease abrasion caused by lateral loads of the emergency spring, increase the motion flexibility of the intermediate shaft by using a single solid rubber bearing member for the intermediate shaft and the adapter plate bearing and also impermeability has been aimed. However the motion flexibility of the rubber bearing design subject to the invention, cause unwanted lateral loads and fluctuations in the force curves and sealing problems and endangers the structural integrity of the spring brake actuator. By using a single solid rubber bearing member in the bearing section, it has been aimed to increase the motion flexibility of the intermediate shaft which is forced to move angularly or radially due to the emergency spring lateral loads, and to decrease the pressure applied onto the bearing section and thus to decrease the abrasion occurring in the bearing means in said bearing section. However increasing the motion flexibility of the intermediate shaft by means of a single solid rubber bearing also increases the radial and angular motion of the intermediate shaft and this leads to axial power losses and to output force fluctuations. Moreover it has been observed that increasing the radial and angular motion of the intermediate shaft, leads to the disruption of contact between the intermediate shaft in the bearing region and the bearing means which in turn leads to impermeability problems. In the present invention a rigid plastic bearing means has been added to the rubber bearing member to provide a two pieced bearing. While sealing is provided at the bearing region by means of the rubber bearing members, it has been aimed to improve the bearing of the intermediate shaft using the rigid plastic bearing means and to decrease the radial and angular motions arising from lateral loads and to prevent axial output force losses and fluctuations. As a result, it has been aimed to strengthen the bearing of the intermediate shaft using the rubber bearing means which provide sealing on its own and which prevents metal-metal contact and decreases abrasion of the bearing and to decrease force losses and abrasion providing sealing using the rigid plastic bearing means which prevents force losses.
Another document known in the state of the art is the patent publication numbered WO9421501A1. In this publication 3 different variants have been explained for center bearing of adapter plate.
The first variant has been shown in the attached FIG. 8, and the explanations in this publication comprise polymer rings and elastomeric impermeability members in the center bearing of adapter plate. The patent application number WO9421501A1 comprises 2 polymer rings (FIGS. 8, 84,86) 2 o-rings (FIGS. 8, 98, 96) and 3 channels (FIG. 8, 90,92,94) to act as bearing for the rings. Besides this, the present invention comprises one rubber sealing means and one form-fit connected rigid plastic polymer ring. And in the present invention there are no o-rings and channels. Sealing is provided by inner sealing rings and outer sealing rings around the rubber bearing member.
In the 2nd and 3rd variants described in the patent application numbered WO9421501A1 the center bearing can be seen in FIGS. 9 and 10. It comprises the described polymer rings (FIGS. 9 and 10, 108,110), o-ring (FIGS. 9 and 10, 114,124,126) and the protrusions and indentations (FIGS. 9 and 10, 102,104) and channels (FIGS. 9 and 10J 120,122). Besides this, the present invention sealing and bearing has been provided without the need for protrusions and indentations on adapter plate, channels and the o-ring.
According to the bearing variants described in the patent application document numbered WO9421501A1 it has been aimed to prevent metal-metal contact of the intermediate shaft and the adapter plate. In the present invention it has been aimed not only to prevent the metal-metal contact of the intermediate shaft and the adapter plate, it has also been aimed to strengthen the bearing between the intermediate shaft and the adapter plate and to decrease lateral loads and force losses.
It is also possible perceive the bearing described in the patent application numbered US2006131116A1 related to the subject of the present invention with the bearing of the known state of the art. The bearing described in this publication has been provided with a monolithic nut ring. In the present patent application is related with two-pieced form-fit bearing comprising rigid plastic and rubber member. The bearing type of the nut ring is different to the bearing of the form-fit rubber member. Moreover in the patent application numbered US2006131116A1 it has been not aimed for the bearing between the intermediate shaft and the adapter plate to be strengthened and for the loss of lateral loads and forces to be decreased.